Apparatus for protecting ac switches and electrical equipment against low temperatures and icing

ABSTRACT

An AC switch comprises blade contacts in which at least one contact member has at least one ferromagnetic portion integrally incorporated therein so that load current passes through the ferromagnetic portion when the switch is closed. The ferromagnetic portion is interposed in series with the remaining portion of the accommodating contact so as to become a component of the operating current electric circuit.

United States Patent 135573141 [72] lnventors Ilya Andreevich Tikhonov;[56] Referen e Cit d Ivan Alexandrovich Dzhanshiev, UNITED STATESPATENTS Lemngradi Anamly 5mm; 1,721,785 7 1929 Meyer l74/128X EduardNikolaevich Yakunin, Velikie Luki,

U.S.S.R. {21] Appl. No. 751,577 [22] Filed Aug. 9, 1968 [45] Patented,Jan. 19, 1971 [73] Assignee Sevem-Zapadnoe ()tdelenie VsesojuznogoGosudarstvennogo Proektno- Izyskatelskogo Nauchno-IssledovatelskogoInstitutaEnergosetpoekt" Leningrad, U.S.S.R.

[54] APPARATUS FOR PROTECTING A.C. SWITCHES AND ELECTRICAL EQUIPMENTAGAINST LOW 511; 174/40, 126, 128; 343/704; 117/235, 240; 335/99, 100,146, 154, 196, 208, 204; ZOO/166C, 162

3,218,384 11/1965 Shaw 174/40 3,249,466 5/1966 Lusher 1 17/235 3,296,3641/1967 Mason 174/126X 3,316,344 4/1967 Kidd et a1. 174/I26X 3,316,3454/1967 Toms et a1. 174/126 3,414,430 12/1968 Maho 1 1 1l7/240X 3,057,97810/1962 335/146X 3,290,630 12/1966 Dyksterhouse et a1. 335/146 FOREIGNPATENTS 1,088,765 10/1967 Great Britain 335/208 469,805 3/1952 Italy174/126 Primary Examiner- A. 3artis Assistant Examiner- Peter W GowdeyAltorneyWaters, Roditi, Schwartz & Nissen ABSTRACT: An AC switchcomprises blade contacts in which at least one contact member has atleast one ferromagnetic portion integrally incorporated therein so thatload current passes through the ferromagnetic portion when the switch isclosed. The ferromagnetic portion is interposed in series with theremaining portion of the accommodating contact so as to become acomponent of the operating current electric circuit.

APPARATUS FOR PROTECTING A.C. SWITCHES AND ELECTRICAL EQUIPMENT AGAINSTLOW TEMPERATURES AND ICING The present invention relates to devices forprotecting AC switchgear and electrical equipment against lowtemperatures and icing.

The device is adapted for use in outdoor electrical installations suchas substations and generating stations, in switchgears, as well as inseparately mounted equipment or apparatus which is under voltage andfeatured by load current flowing therethrough (for example, atdisconnector knife blades of disconnecting and isolating switches, atcircuit breaker contacts, inputs into apparatus and premises, etc.) andwhich is installed in regions with low temperatures and is likely tobecome subject to icing.

The experience of servicing the outdoor electrical installations undercold climatic conditions shows that low tempera tures, icing andice-crusted formation frequently interferes with normal functioning ofthe electrical installations any may even be the cause of a breakdown.

- Besides, under low temperature conditions (from 30 C. below zero to 60C. below zero) due to contraction of the cooled metal, the knife bladesof disconnecting switches or isolating switches freeze" to the contactjaws and are not capable of moving therefrom upon receiving a pulse fora disconnecting operation with the result that the apparatus is notdisconnected. The analogous phenomenon is observed when icing takesplace.

Moreover, the layer of ice thus formed on the current carrying membersmakes the construction heavier, and increase wind load onto thecurrent-carrying members. Due to the fact that low temperatures, frostand icing are observed over a large part of the globe, said phenomenaare the cause of considerable damage to electrical installations.Therefore, taking into consideration the intensified development ofterritories in extreme northern and southern areas of both hemispheresit becomes a very urgent matter to preclude electrical installationsfrom the effect of the above-mentioned phenomena.

If failures in operation of operating mechanisms of disconnectingswitches, isolating switches and etc., caused by low temperatures can beprevented by the choice-of a grease or lubricant with a low freezingpoint or by mea'fis of local heating, there exists no simple andreliable rheans to prevent failures in operation of contact systemsfunctioning under high voltages, say in high-voltage installations.

Conventional devices adapted to preclude freezing and icing of switchessuffer from a number of disadvantages and are inconvenient in service aswill be explained hereinafter.

Thus, the electric heating by means of electric furnaces andtubular-heating elements with ohmic resistance is not practicable due tothe difficulty in power supply and the danger of a breakdown. Heating bywarm air delivered from an external heating source is constructionallycomplicated and is expensive, therefore, it has found no application inpractice. I

Moreover, ice breaking by virtue of a blow torch suspended from aninsulated rod as well as chopping the ice mechanically offers greatdifficulties.

The devices adapted to prevent icing of split contacts of electricalapparatus by means of mechanical destruction of the crust of ice requireincreased mechanical efforts and are effective only in cases where thethickness of ice is not in excess of a particular value. Moreover, theabove-mentioned devices fail to prevent freezing of contacts under lowtemperature conditions. Apart from this, said devices cannot be employedin contact systems of high-speed disconnecting apparatus such as circuitbreakers, isolating switches, etc. since the disconnection moment ofsaid apparatus from the relay protection is not known beforehand whichmay lead to a breakdown.

More reliable and reasonable are devices capable of preventing icing andfreezing of the component units of the electrical equipment andapparatus.

A device featuring a short-circuited aluminum turn isolated from thewire, adapted to prevent icing of conductors of the transmission linesis constructionally inconvenient for the equipment employed atsubstations.

It is a primary object of the present invention to eliminate theabove-mentiond disadvantages.

The invention is aimed at the development of a device for protectingelectrical equipment against low temperatures and icing which shall besimple in design and reliable in operation and shall prevent freezing ofcurrent carrying members of the apparatus involved and icing thereof byvirtue of electrical heating of the apparatus in question.

According to the invention, said object is accomplished by the fact thatin the device for protecting AC switchgear and electrical equipmentagainst low temperatures and icing by resorting to heating of theequipment or apparatus involved by electrical-heating elements, saidheating elements are essentially ferromagnetic bodies which are so fixedon the equipment or apparatus involved that they are subject to heatingby the magnetic field created by the load current flowing through theprotected equipment.

The ferromagnetic bodies, which are essentially electricalheatingelements, may be of such a shape and be mounted so as to embrace a partof the protected equipment or apparatus completely or partially.Moreover, the ferromagnetic bodies may be formed by a coating of thematerial applied upon the protected equipment or apparatus and featuringferromagnetic properties.

It is expedient that the magnetic bodies be made detachable, be insertedinto the circuit of the operating current of the protected equipment orapparatus, and be made use of as members of the current-carryingcircuit.

The advantages of the herein-proposed method are: simple implementationof the invention in contemplation both for manufacturing new apparatusand for increasing the operational reliability of already manufacturedand mounted apparatus; high efficiency; and great reliability with nopossibility of an electric breakdown in the high-voltage installations.

The invention will be more apparent from the following description ofexemplary embodiments thereof, reference being made to the accompanyingdrawings, wherein:

FIG. 1 represents an elementary diagram of the device, according to theinvention, wherein a plate is used as a ferromagnetic body;

FIG. 2 represents an elementary diagram of the device, according to theinvention, wherein a coating of a material featuring ferromagneticproperties is used as a ferromagnetic body;

FIG. 3 shows the dependence of induction of the ferromagnetic body oncurrent flowing through the protected equipment or apparatus; and

FIG. 4 is an elementary diagram of the device, according to theinvention, wherein a ferromagnetic body is series-connected into thecircuit of the operating current flowing through the protected equipmentor apparatus,

Heating of ferromagnetic bodies made of steel, cobalt and of a number ofalloys is due to energy release of hysteresis and eddy current lossescaused by the variable magnetic field created by the load currentflowing through the protected equipment or apparatus. The heat thusevolved in said ferromagnetic bodies either raises the temperature ofthe components of the apparatus involved and prevents ice-crustformation, excessive cooling and *freezing" of contacts or melts the iceformed.

The ferromagnetic bodies may vary in shape depending upon theconfiguration of the equipment or apparatus to be protected.

The energy released by the ferromagnetic body can be calculated from thefollowing expression:

P=SHe where;

Taking into consideration the local conditions as well as the value ofthe current involved, the rate of cooling, theambient temperature, andthe maximum permissible temperature, the characteristics of theferromagnetic body are determined to maintain the above-zero temperatureof the protected apparatus such as a contact knife blade of an isolatingor disconnecting switch, capable of preventing saidapparatus-fromfreezing or icing.

The ferromagnetic bodies fixed in position on the protected equipment orapparatus may feature movable parts which can be replaced with respectto the main portion of the ferromagnetic body which fact provides forthe possibility to control the quantity of the heat evolved in theferromagnetic body depending upon the required conditions.

The evolution of heat in the ferromagnetic body occurs with the currentflowing therethrough, i.e. the evolution of heat is always ensured'inthe most critical circuits which cannot be disconnected. In particular,with low temperature operating conditions, power transformers aregenerally never cut off for fear of oil freezing, stoppage ofcirculation and subsequent local overheating when the transformer isswitched into the circuit again. i v

The disconnecting switches which are not alive, such as those insertedin the circuits to the gap cells, as a rule, are not critical componentsand are seldom involved in operation. Therefore, to break the ice formedon the above-said disconnecting switches or to warm them up they may becut off if required.

Let us consider a number of embodiments of the devices adapted toprotect AC switchgear and electrical equipment against low temperaturesand ice deposition.

Referring to FIG! 1 it can be seen that thedevice is employed in ahorizontal disconnecting switch featuring a lefthand blade land aright-hand blade -2. For the sake of simplicity the lamellas providingfor the contact, as well as the insulators and the fastening parts arenotshown in the drawing.

The blade 1 carries (without insulation) a ferromagnetic body 3 which isessentially a plate embracing the blade 1. .A similar plate may embracethe blade 2 (as'it is shown in FIG 1) if one plate fails to provide forsafe protection.

The heat from the ferromagnetic bodies when the load current flowsthrough the disconnecting switch in .question is transferred to theblades '1 and 2 of the disconnecting switch and prevents ice-crustformation on said blades and excessive cooling thereof. I

In addition to the disconnecting switch, isolating switches,

the contacts of circuit breakers, as well as inputs into apparatus ordwellings and other electrical equipment subject to low temperatures andice-crust formation be protected, and plates, rings, sleeves, clamps,endpieces or tips may serve as the ferromagnetic bodies.

Now referring to FIG. 2the blades 1 and are applied with a coating of amaterial featuring ferromagnetic properties. Said coating serves as aferromagnetic body. Ferromagnetic enamels, paints and varnishes may beused as the above-said ferromagnetic coating. 7 i

in cases when the range of the value of the current flowing through theprotected apparatus is considerable, the ferromagnetic bodies in theherein-proposed device are so selected that they are magneticallysaturated within the required portion of the range of the operatingcurrent fluctuations. i

' All the above-said will be more apparent when referring to FIG. 3wherein plotted on the X-axis is the current I flowing through theapparatus protected by a ferromagnetic body whereas plotted on theY-axis is the induction of the ferromagnetic member Be.

The characteristics of the ferromagnetic body are so selected that theconditions of the magnetic saturation occur at a minimum possible valueof the operating current l Thus, in case of operating currentfluctuations within the full stantially change, therefore, the power ofthe electromagnetic losses is kept almost constant with the resultthat-the efficiency of heating will not practically depend upon thecurrent involved. The ferromagnetic bodies are made of ferromagneticmaterials or magnetic alloys featuring increased hysteresis and eddycurrent losses and capable of saturating with preset currentfluctuations.

The presence of ferromagneticb'odies in the magnetic field of theprotected apparatus through which the current flows causeselectrodynamicforces both between the ferromagnetic bodies and betweenthe conductor and each of the ferromagnetic bodiesinvolved.

Taking in consideration the above-mentionedfact, an embodiment of thedevice provides for such an arrangement of the ferromagnetic bodieswithrespect to each other and to the conductor that the arisingelectrodynamic forces contribute to an increase of the electrodynamicstability of the entire system.

For example, the electrodynamic forces may be directed to increasethecontact pressure ofthc detachable contacts in the apparatus withtheshortcircuit current involved.

In a number of cases the opportunity arises to simplify or to dispensewith the construction elements of the apparatus which were speciallyadapted to provide forelectrodynamic stability of the apparatus therebymaking it more simplified and inexpensive. I I

The introduction of the ferromagnetic bodies into the current conductingsystems results in. some increase in weight of the equipment and inconsumption of material. Moreover, the introduction of ferromagneticbodies ;in the moving parts of the high-speed apparatus mayresultinsomed'ecrease of speed response.

To eliminate the above-said, the device. provides in some cases for thepossibility. to extend the functions of the ferromagnetic bodies by.inserting the "latter into the operating current electric circuit ,ofthedevice-under protection or by employing said bodies as elements ofthe currenbconducting circuit such as current COHdUClOTSyCOIlKfiCl-S,contact plates, lamellas, clamps, means for creating contact pressureetc., as it is shown in H6. 4 where a ferromagnetic body 3 isconstituted as a portion of the, left-handblade 1 and is in seriesconnection with the adjoiningportions of blade 1.

Such a combination of functions makes it possible to decrease the numberof components of the device and the weight of the construction.

The herein-disclosed device and the modifications thereof, inparticular, may be employed at the contact systems of isolatingswitches, i.e. disconnecting switches capable ofautomatically cuttingoff no-load current flowing through the equipment or apparatusinvolved-since this is one of the most urgent problemsto provide for aserviceability thereof under the cold environmental conditions. The mostdistinguished feature of the herein-proposed .device is that it can beemployed in regions where most intensive ice formation is likely tooccur as the above-said device is generally adapted to prevent any iceformation.

In regions having warm summers and cold winters, the ferromagneticbodies may be made detachable and be mounted on the apparatus in the.cold season only.

We claim:

1. AC switch apparatus comprising contact members having open and closedstates, at least one member at including at least one ferromagneticportion integrally incorporated therein at an intermediate locationproviding portions on op posite sides thereof so that load currentpasses through said ferromagnetic portion when the members are in aclosed state, said one contact member having a substantially uniformcross section throughout its length both through the ferromagneticportion and said portions on opposite sides thereof.

1. AC switch apparatus comprising contact members having open and closedstates, at least one member at including at least one ferromagneticportion integrally incorporated therein at an intermediate locationproviding portions on opposite sides thereof so that load current passesthrough said ferromagnetic portion when the members are in a closedstate, said one contact member having a substantially uniform crosssection throughout its length both through the ferromagnetic portion andsaid portions on opposite sides thereof.